It's one thing to lose market share -- which Yahoo has been doing consistently for the last year. But even when search companies swap market share, the overall search market has been growing so fast that they usually gain in absolute terms.

But Yahoo's absolute query volume dropped 5%, according to ComScore.

Analyst Ben Schachter at Macquarie Capital points out that this is particularly damaging because Yahoo's search business requires zero effort -- the company outsourced it to Microsoft in 2009 -- and yet Yahoo keeps around 90% of the revenue from each search. Schachter estimates that "most" of Yahoo's EBITDA earnings come from search.

In other words, Yahoo's most profitable business is slowly collapsing.

Macquarie also cautions that it sees no structural bottom for Yahoo's search decline.

Here's the updated market share chart for the three leaders for the last 12 months. Google and Bing were unchanged since last month, Yahoo was down. Note that this is U.S. only, and doesn't include mobile search, otherwise Google would be even more dominant.